The invention relates to a signal distribution cable network which comprises a network head end and at least a cable along which at least a signal processing device is inserted. The invention also relates to said signal processing device and also to an equalizing device that may be used in such signal processing device.
The invention notably applies to very broadband networks (40 MHz-860 MHz) for cable television signal distribution networks.
U.S. Pat. No. 4,250,459 describes an equalizing device comprising a first branch having a high-pass filter serially connected with an adjustable attenuator and a second branch comprising a resistor. Such a device is used in a cable distribution network in order to compensate for the attenuation introduced by the cable on the transmitted signals, notably on the high frequencies.
The invention proposes another embodiment of such an equalizing device intended to be used for another application.
An equalizing device according to the invention comprises a first and a second branch which are connected:
at the input via a signal separation device intended to separate the frequencies of an input signal for producing a signal that occupies a first frequency band via the first branch, and a signal that occupies a second frequency band via the second branch,
and at the output via a recombining device intended to produce an output signal that occupies the first and second freguency bands based on the signals transmitted by the first and the second branch, wherein the first and second frequency bands correspond to a cutting off of a useful frequency band between a low part and a high part the first and second branches each include at least an attenuator, while the attenuation of the first attenuator is higher than that of the second attenuator, and the separation and recombining devices having a passband designed in such a way that the output signal has a substantially constant amplitude in said first and second frequency bands.
The invention thus comprises separating the input signal so as to separately process a first and a second frequency band. The intended processing is an attenuation of the signal. Equalizing the signal by attenuating it permits to avoid the problems of saturation and noise, and also to reduce the consumption of the equalizing device. The attenuation caused by the first and/or second branch varies in frequency. This frequency variation is determined by the passband of the separation and combining devices.
The invention advantageously applies to the particular case where a VHF distribution network is made to evolve into a very broadband distribution network. The VHF distribution networks utilize passive components which may cause faults to occur in the very high frequency bands. These faults lack amplitude. They vary with frequency. If one makes a VHF network evolve into a very broadband network, these passive components are thus to be replaced, which is expensive. This replacement may be avoided by utilizing a first embodiment of an equalizing device according to the invention. The equalizing device of the invention delivers an output signal which has a constant amplitude. Advantageously, the second attenuator is an adjustable attenuator which can have a local or remote control. The attenuation caused by the second attenuator may thus be adapted on a case-by-case base as a function of the distribution network, to compensate exactly for really introduced faults.